The present invention is directed to an air supported belt conveyor, and in particular to an air supported belt conveyor having a conveyor belt and a multipressure plenum system including a multipressure plenum and a multipressure air supply system adapted to provide low pressure air or high pressure air as needed to the multipressure plenum to support the conveyor belt above the multipressure plenum.
Air supported belt conveyors are subject to overloading in the impact zone of the conveyor where the conveyed material is loaded onto the conveyor belt. The overloading of conveyed material can be due to surge loading, the use of a conveyor chute as a hopper, or from various conveyor and conveyor chute designs or operating methods that result in a greater load being placed on the conveyor belt than the design capacity of the belt. The overload of conveyed material can be intermittent or constant, and can vary greatly in magnitude. Air supported conveyors are capable of handling varying loads of conveyed material, but normally the low pressure air supply system and the plenum which receives the low pressure air are designed for the design capacity of the belt. Designing the plenum and air supply system for worst case material overload situations results in an over design that is energy inefficient, that can create unnecessarily high volumes of air being passed through the plenum which generates dust, and that can create unnecessarily high air pressures that may cause an unloaded conveyor belt to be unstable.
While air supported conveyors can handle an occasional overload of conveyed material, the inability of air supported conveyors to handle overloads has limited them to applications with fairly consistent loading conditions. When an air supported conveyor is loaded beyond the capacity of the conveyor to maintain a cushion or film of air between the plenum and the conveyor belt, the belt comes into contact with the plenum and frictional forces opposing movement of the belt increase dramatically. The increase in frictional forces causes the drive system of the conveyor to draw more power, and may cause the motor overload protection to stop the conveyor. This creates a situation where the operator of the conveyor must resolve the overload problem, usually by manually digging out conveyed material from the impact zone of the conveyor and then restarting the conveyor.
Overload conditions occur with conventional idler roller conveyors, but idler roller conveyors are more tolerant of overloads than air supported conveyors because the additional load that is placed on the roller bearings in an idler roller conveyor does not result in a dramatic increase in the frictional forces that oppose movement of the belt. Both conventional idler roller conveyors and air supported conveyors have difficulty overcoming the internal shearing force of the conveyed bulk material and the friction of the bulk material with the conveyor chute and skirt walls of the conveyor, when the conveyor feed system becomes plugged. Plugged conveyor chutes are one of the common situations that result in an overload in the impact zone of a conveyor. Other common causes include mistakes in operation of the conveyor, such as increasing the flow rate of conveyed material above the flow capacity of the conveyor, or conveying a type of bulk material on the conveyor that is outside of the material specifications for which the conveyor was designed. The conveyor chute may also become plugged by foreign material or tramp iron becoming wedged in the conveyor chute or impact zone of the conveyor. Controls have been designed to prevent plugging of conveyor chutes and impact zones, such as chute level indicators and flow rate indicators. However, these indicator controls are often inoperative. The multipressure plenum system disclosed herein enables an air supported conveyor to switch from a low pressure air supply to a high pressure air supply in the impact zone plenum when a material overload situation is sensed or predicted to thereby enable the conveyor to continue running efficiently.